Browsing by Author "McConnell, JR"
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- ItemDating Antarctic ice cores using high-temporal resolution black carbon records(Antarctic Climate and Ecosystems Cooperative Research Centre, 2016-03-07) Edwards, R; Vallelonga, P; McConnell, JR; Bertler, NAN; Curran, MAJ; Sigil, M; Fudge, TJ; Anschuetz, H; Neff, PD; Emanuelsson, D; Bisiaux, M; Goodwin, D; Smith, AM; Taylor, KC; Moy, AD; Fetieng, W; Ellis, ABlack carbon aerosols (BC) emitted by fires in the Southern Hemisphere (SH) are transported to Antarctica and preserved in the Antarctic ice sheet. Recent efforts to develop ice core records of BC deposition to Antarctica show variability in BC over a broad range of time scales. The ~ monthly-resolution BC record from the WAIS divide deep ice core displayed strong seasonal variability in modern sections of the record consistent with the timing of SH biomass burning. The record was subsequently used as an annual layer dating proxy in conjunction with other chemical species. If the emissions and transport of BC to Antarctica are stable over long periods of time it may be useful as an annual layer proxy at sites other than WAIS. To date, a rigorous comparison of Antarctic ice core BC seasonality from different locations have not been conducted. Here we present a comparison of BC ice core data from the top sections of the WAIS divide deep core, the Roosevelt Island RICE core, and the Law Dome DSS1213 core. The RICE and Law Dome sites are separated from WAIS by large distances and experience different atmospheric circulation and climate regimes. A detailed description of the data uncertainties and its use in annual layer counting will be discussed.
- ItemSolar and climate influences on ice core 10Be records from Antarctica and Greenland during the neutron monitor era(Elsevier, 2012-11-15) Pedro, JB; McConnell, JR; van Ommen, TD; Fink, D; Curran, MAJ; Smith, AM; Simon, KJ; Moy, AD; Das, SBCosmogenic 10Be in polar ice cores is a primary proxy for past solar activity. However, interpretation of the 10Be record is hindered by limited understanding of the physical processes governing its atmospheric transport and deposition to the ice sheets. This issue is addressed by evaluating two accurately dated, annually resolved ice core 10Be records against modern solar activity observations and instrumental and reanalysis climate data. The cores are sampled from the DSS site on Law Dome, East Antarctica (spanning 1936–2009) and the Das2 site, southeast Greenland (1936–2002), permitting inter-hemispheric comparisons. Concentrations at both DSS and Das2 are significantly correlated to the 11-yr solar cycle modulation of cosmic ray intensity, rxy=0.54 with 95% CI [0.31; 0.70], and rxy=0.45 with 95% CI [0.22; 0.62], respectively. For both sites, if fluxes are used instead of concentrations then correlations with solar activity decrease. The strength and spectral coherence of the solar activity signal in 10Be is enhanced when ice core records are combined from both Antarctica and Greenland. The amplitudes of the 11-yr solar cycles in the 10Be data appear inconsistent with the view that the ice sheets receive only 10Be produced at polar latitudes. Significant climate signals detected in the 10Be series include the zonal wave three pattern of atmospheric circulation at DSS, rxy=−0.36 with 95% CI [−0.57; −0.10], and the North Atlantic Oscillation at Das2, rxy=−0.42 with 95% CI [−0.64; −0.15]. The sensitivity of 10Be concentrations to modes of atmospheric circulation advises caution in the use of 10Be records from single sites in solar forcing reconstructions. © 2012 Elsevier B.V.
- ItemTowards 14C-dating of gases in ice cores – constraining the in situ cosmogenic 14C production rates by muons(Australian Nuclear Science and Technology Organisation, 2021-11-17) Dyonisius, MN; Petrenko, VV; Smith, AM; Hmiel, B; Neff, PD; Yang, B; Hua, Q; Place, PF; Menking, J; Shackleton, SA; Beaudette, R; Harth, CM; Kalk, M; Roop, H; Bereiter, B; Armanetti, C; Buizert, C; Schmitt, J; Brook, EJ; Severinghaus, JP; Weiss, RF; McConnell, JRRadiocarbon dating of glacial ice has been a longstanding goal in ice core science. In glacial ice, ¹⁴ C is incorporated mainly through trapping of ¹⁴ C-containing atmospheric gases (¹⁴ CO₂ , ¹⁴ CO, and ¹⁴ CH₄ ). However, ¹⁴ C in ice is also produced in situ, directly in the ice lattice from reactions with secondary cosmic rays. In situ ¹⁴ C in ice mostly accumulates after bubble close-off (generally at firn depths between 50-120 m) because almost all of the in situ produced ¹⁴ C in the firn column is lost to the atmosphere via diffusion. The in situ ¹⁴ C at corresponding close-off depths of most ice core sites is generally dominated by production from deep penetrating muons. Understanding the muogenic ¹⁴ C production rates is thus important to deconvolve the in situ cosmogenic and atmospheric ¹⁴ C signals in ice cores. In this study, we use measurements of ¹⁴ C in ancient ice (>50 kilo-annum before present, ka BP) from the Taylor Glacier ablation site, Antarctica to calibrate the muogenic ¹⁴ C production rates. We find that literature values are overestimated by factors of 5.7 (3.6-13.9, 95% confidence interval) and 3.7 (2.0-11.9 95% confidence interval) for negative muon capture and fast muon interactions respectively. Furthermore, the partitioning between the in situ ¹⁴ C species appears to be constant (¹⁴ CO:¹⁴ CO₂ ratio of 1:2, with small <0.2% contributions from ¹⁴ CH₄ ). Our results allow for future ice core ¹⁴ C studies to be potentially used for several applications, including absolute dating of gases and improving the ¹⁴ C calibration curve in periods where high-resolution tree ring data are not available.
- ItemUsing ice core measurements from Taylor Glacier, Antarctica to calibrate in situ cosmogenic 14C production rates by muons(Copernicus Publications, 2022-01-26) Dyonisius, MN; Petrenko, VV; Smith, AM; Hmiel, B; Neff, PD; Yang, B; Hua, Q; Schmitt, J; Shackleton, SA; Buizert, C; Place, PF; Menking, JA; Beaudette, R; Harth, CM; Kalk, M; Roop, H; Bereiter, B; Armanetti, C; Vimont, I; Michel, SE; Brook, EJ; Severinghaus, JP; Weiss, RF; McConnell, JRCosmic rays entering the Earth’s atmosphere produce showers of secondary particles such as neutrons and muons. The interaction of these neutrons and muons with oxygen-16 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). Analyses of in situ produced cosmogenic 14C in quartz are commonly used to investigate the Earth’s landscape evolution. In glacial ice, 14C is also incorporated through trapping of 14C-containing atmospheric gases (14CO2, 14CO, and 14CH4). Understanding the production rates of in situ cosmogenic 14C is important to deconvolve the in situ cosmogenic and atmospheric 14C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14C production rates by muons (which are the dominant production mechanism at depths of > 6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14C in ancient ice (> 50 kilo-annum before present, ka BP) from the Taylor Glacier ablation site, Antarctica in combination with a 2D ice flow model to better constrain the rates of 14C production by muons. We find that the commonly used values for muogenic 14C production rates (Heisinger et al., 2002a, 2002b) in ice are too high by factors of 5.7 (3.6–13.9, 95 % confidence interval) and 3.7 (2.0–11.9 95 % confidence interval) for negative muon capture and fast muon interactions, respectively. Our constraints on muogenic 14C production rates in ice allow for future measurements of 14C in ice cores to be used for other applications and imply that muogenic 14C production rates in quartz are overestimated as well. © Author(s) 2022.